BM 3.8 sp5 on nw6.5sp5

have a user that is having problems accessing a group calendar on yahoo groups. It appears to be a caching issue. User gets into the calendar feature, and tries to change the view to a different format (week, month, year), or a different date, and the initial page just gets reloaded, showing "today's" day calendar.
It works correctly on a machine connected outside the firewall.

tried to set up a non-cacheable url pattern for "yahoo.com"...then tried "*.yahoo.com"...then "*.yahoo.com/* etc , etc....can't get it to work. (did unload proxy/load proxy-cc, deleted temp internet files on the workstation, too). I used rtmonitor to review the url's being accessed, in case there was a re-direct...there wasn't any that I could see. The url's for the different calendar pages seem to have a "?" in them, so the shouldn't be getting cached, anyway, (should they?).
also tried a firefox browser instead of IE...no difference.
Found some talk about the proxy.cfg file and yahoo...so I went in there and set the sendhttp11request=1 to "o"...(unload/reload proxy)...no change. tried the latest proxy.cfg (version 30) from 29...no change.

this stuff used to work a few months ago, according to the user. I imagine that my latest round of patching did something...but I don't know what.
any thoughts?